A federal judge has refused to block enforcement of the state's shark fin sales ban, rejecting arguments that the law discriminates against Chinese Americans.

The law serves a legitimate local purpose based on concerns that shark finning, in which fins are removed from caught sharks and the carcasses thrown back into the water, kills millions of sharks annually, causing a serious threat to the ocean ecosystem, U.S. District Judge Phyllis Hamilton in Oakland said in a written ruling Wednesday.

"Plaintiffs have provided no evidence that the law was enacted for the purpose of discriminating against Chinese Americans," Hamilton ruled. "Plaintiff's own evidence shows that only a small percent of Chinese Americans eat shark fin soup regularly, and that approximately half of Chinese Americans actually support the Shark Fin Law."

San Francisco's Chinatown Neighborhood Association and another group representing Chinese Americans and businesses whose cultural practices involve using shark fins sued to challenge the law, which took effect a year ago. The groups said the law violates constitutional equal protection and other rights.

California's shark fin sales ban, passed by the Legislature in 2011, bars restaurants from selling any newly acquired shark fins starting July 1 of this year.

People of Chinese descent have had to forgo participating in the ancient tradition of serving shark fin soup at banquets, and the law doesn't protect sharks because it's still legal to kill them, lawyers for the groups said in court papers.

Restaurant owners, merchants and importers have lost hundreds of thousands of dollars in the past year due to lost sales of shark fin soup and shark fins, according to documents submitted by the plaintiffs. One Millbrae restaurant could lose $100,000 a year, while another in Daly City expects to lose more than $850,000 a year, Hamilton said, citing plaintiffs' claims.

"We are disappointed in the ruling, but we realize that the legal standard for preliminary injunction is very high," said Jill Diamond, an attorney for the plaintiffs. "We remain optimistic about the case and are prepared to move forward until we prevail."